1. Field of the Invention
The present invention relates generally to a chair of the type suitable for use in an office environment and, more particularly, to a reclining office chair having several structural and operating features which offer a number of ergonomic advantages over the prior art.
2. Description of the Related Art
Over many years attempts have been made to design chairs for use in office environments which are comfortable to use and thereby avoid user fatigue over prolonged use. In one simple form a chair may be provided with a swivel base for ease of turning and include a control mechanism which permits the chair to rock. A disadvantage of these relatively simple chairs is that conjoint rocking motion of the chair seat and back naturally lifts the user""s feet off the floor, which can create stability problems and place upward force on the front of the user""s thighs which can reduce fluid circulation in the user""s legs.
To improve on the foregoing chair construction, chair controls are known which provide for synchronous movement of the chair seat and back. Where office chairs are concerned, a xe2x80x9csynchronous controlxe2x80x9d means the arrangement of a combined or dependent back adjustment and seat adjustment, that is to say the adjustment of the back inclination fundamentally also results in an adjustment of the sitting surface. An example of a synchronous chair control is disclosed in U.S. Pat. No. 5,318,345, issued to Olson and assigned to the common assignee herein. With the aforementioned Olson control, the chair back is designed to tilt at one predetermined rate of recline while the seat tilts synchronously at a much lesser rate. The result is that the user""s feet are not lifted from the floor when the back is reclined. Also, fluid circulation in the user""s legs is not interrupted by substantial upward movement of the forward end of the seat. Another advantage of this control is that undesirable xe2x80x9cshirt pullxe2x80x9d is minimized by the strategic location of the tilt axis. Other examples of synchronous chair controls are disclosed in U.S. Pat. Nos. 5,366,274 and 5,860,701 to name a few.
Another feature embodied in recently designed office chairs that offers considerable ergonomic advantages is a tilt limiter feature for the chair back. With such a mechanism built into the chair control, the user may selectively set the degree of back recline at a predetermined angle thereby adding to comfort as the chair is used. An example of such a tilt limiter mechanism is disclosed in U.S. Pat. No. 6,102,477 issued to Kurtz and assigned to the common assignee herein. This particular mechanism offers the advantage of providing for infinitely variable angles of tilt within a predetermined overall range. The mechanism is also highly cost-effective to construct.
Yet another feature of current ergonomically designed chairs is the provision of height and pivot adjustable arm pads. Such a feature is particularly advantageous in providing the user with additional support to the arms, forearms, wrists and shoulders in order to minimize repetitive stress injuries when the user is keyboarding, for example, while seated in the chair. An example of such an adjustable arm pad is disclosed in U.S. Pat. No. 5,908,221 issued to Neil. One advantage of the ""221 structure is that it uses gas cylinders for arm pad height adjustment and thus is easily adjusted with the push of a single button.
Yet another feature of current ergonomically designed office chairs includes an adjustable lumbar support mechanism for providing preselected chair back tension in the region of the user""s lower back. An adjustable lumbar support allows the chair user to select a comfortable level of pressure on the lower back depending upon the specific office task being performed. Such a mechanism is disclosed, for example, in U.S. Pat. No. 5,797,652.
Still another feature of certain ergonomically designed office chairs, particularly of recent vintage, is the incorporation of fabric mesh into the construction of the chair seat, and/or back. While mesh materials are well-known in the construction of lawn furniture seating, it has only been relatively recently that such materials have been used successfully in office seating. These materials offer the advantage of enhanced air circulation for and consequent heat transfer from the chair user""s body, which can improve the comfort of the chair. An example of the use of such fabric mesh in an office chair is disclosed in U.S. Pat. No. 6,125,521 issued to Stumpf et al.
Yet another feature of certain ergonomically designed chairs is the provision of a seat cushion having the capability of effecting heat transfer from the chair user""s buttocks area while at the same time offering comfort to the user while seated, together with adequate support. Known seat cushions having such capability may involve a passive or active air flow circulation feature of the type disclosed, for example, in U.S. Pat. No. 6,179,706.
The present invention provides a totally redesigned ergonomic chair that incorporates improved functional aspects in all areas of a modular chair construction and in its use, including tilt limit control, seat adjustment, arm adjustment, lumbar support, cushion airflow, mesh attachment and modular base frame assembly.
The various subfeatures of these modular components are the subject of the following individual applications filed of even date herewith, all commonly assigned, the disclosures of which are incorporated in full by reference:
Multi-position Tilt Limiting Mechanism, application Ser. No. 09/882,500
Locking Device for Chair Seat Horizontal Adjustment Mechanism, application Ser. No. 09/881,896.
Height and Pivot Adjustable Chair Arm, application Ser. No. 09/881,818.
Lumbar Support for a Chair, application Ser. No. 09/881,795.
Body Support Member, application Ser. No. 09/882,503.
Chair Back Construction, application Ser. No. 09/882,237.
Chair of Modular Construction, application Ser. No. 09/881,897.
In each of these cases, features combine to provide an overall chair that is a significant improvement over the prior art.
Thus, for example, the present invention provides a reclining chair having a four bar linkage system that causes the rear of the seat to elevate as the back is reclined lending an unusual and comfortable balance during reclining. A tilt limit control conveniently and effectively limits the degree of chair back tilt to one of three reclined positions by manual movement of a simple lever. Horizontal positioning of the chair seat cushion is accomplished using a simple locking device that allows the chair user to simply lift up on the front of the cushion and select a preferred horizontal cushion position. Height and pivot adjustable chair arms are actuated with the push of a button by gas cylinders lending convenient adjustment to suit a specific work task. A lumbar support is easily height adjustable, by providing tension to the back frame and requires no screws or adjustment knobs in its adjustment mechanism. A modular cushion includes a comfortable heat absorbing gel layer and is vented uniquely for air circulation. The back of the chair is of fabric mesh construction and includes a novel attachment system for superior comfort. The base of the chair is of modular construction that provides for ease of assembly and lends rigidity to the chair construction.
The present invention improves over the prior art by providing an ergonomic chair having a four-bar linkage arrangement wherein a lower frame member is provided with a rigid front support and a rigid rear support with a seat member pivotably connected to the front support. A back rest has an upper support pivotably connected at an upper end of the rear support of the lower frame member. A link member pivotably connects at a first end to a rear support of the seat member and at second end to a lower support of the back rest. This novel arrangement permits tilting movement of the backrest rearwardly relative to the lower frame member causing elevation of a rear portion of the seat member, permitting the feet to remain on the floor and alleviating pressure on the user""s thighs. This is accomplished by a linkage mechanism creating an instantaneous center of rotation of the chair seat and back that is approximately at the user""s hip. A further advantage is that the movement of the seat and back reduces undesirable xe2x80x9cshirt pull.xe2x80x9d Still further, the user sitting in the chair will feel a weight reduction effect as a result of lift of the seat back during reclining. The apparent weight reduction will be sensed as lightness and give the feel of comfort.